A hydrofracturing process, also known as “hydrofracing”, can be used for stimulating oil/gas well production and entails pumping a viscous hydraulic liquid (known in the industry as a “pad”) into a well. The intent of the hydrofracing is to fracture geologic formations and expose isolated beds of hydrocarbons around the well, thereby increasing per well volumes of extractable material such as oil, natural gas, etc.
Following or concurrent with an initial liquid injection, a slurry of surfactants, acids, and solid particles typically having diameters between 500-2000 microns is added to the well. The purpose of this slurry is to selectively open, clean and finally prop open the resultant fractures, with the particulates commonly referred to as proppants.
Proppants in the slurry remain in an appropriate location after the release of a fracturing pressure. With down well pressures often greater than 5000 pounds per square inch, cleaning and re-fracturing of wells incurring extremely high costs and the extractable materials back-flowing through the remaining proppants, the particulates must exhibit suitable strength, reliability and permeability.
A wide range of proppant materials have been used over the years in hydrofracturing, ranging from ground walnut hulls and Ottawa White Sands to synthetic materials comprised of high alumina content kaolin and bauxite ores which have been processed into roughly spherical form via relatively expensive high temperature sintering routes. For example, U.S. Patent Application Publication No. 2004/0148967 by Celikkaya et al. discloses a method of making ceramic particles that have an average hardness of at least 13 gigapascals using a glass that contains at least 35 weight percent Al2O3. In addition, the hydrofracturing industry continues to seek stronger, lower specific weight and cheaper alternatives to enhance the efficiency and lower the costs of stimulating oil/gas wells.
Proposed key features or properties of suitable proppants are: low cost; high strength and high degree of sphericity to promote flow and dispersion in the fracing pad; low specific gravity to mitigate settling during placement; and highly reliable failure behavior to promote maximum well permeability. For example, U.S. Patent Application Publication No. 2009/0082231 by Shmotiev et al. has disclosed a method for increasing the strength of glass spheres for producing a proppant, the proppant having at least 40 percent crystalline phase.
Glass spheres are an attractive candidate for use as proppants based on their commercial abundance, ease of manufacture, low cost, and high strength. Candidate materials that meet most of the proppant requirements are spheroidized glass manufactured from industrial byproduct waste streams such as mixed glass cullet, rhyolite, basalt, tholeiite, olivine and/or andesite. However, the utility of glass spheres produced from such raw materials has been hampered by their propensity to fail energetically and catastrophically into small fragments, which effectively “blind” the well. Currently, the use of glass, natural or otherwise, is not practiced for this reason. As such, a process for producing relatively inexpensive and yet adequate proppant particulates would be desirable.